Acoustic surface wave filter

Abstract

An acoustic surface wave filter comprises a member stimulable to surface oscillations with means for converting electrical energy into mechanical energy and vice versa associated therewith and a plurality of disturbance locations on a surface of the member in the form of a line grating with variable spacing between adjacent lines in the longitudinal direction of the lines.

What is claimed is: 
     
       1. An acoustic surface wave filter comprising at least one member which can be stimulated to surface oscillations and is made at least partly of piezoelectric material, disturbance locations for surface waves on the surface on at least one side of the said member and means, associated with said member, for converting electrical energy into mechanical energy and vice versa, at least some of the disturbance locations being combined into a resonator in the form of a line grating and the average distance between the disturbance locations in the resonator being equal to half the wave-length of the surface waves or an integral multiple thereof, characterised in that the distance between successive grating lines or between opposite portions of the lines, at least in one part of the resonator, varies in the longitudinal direction of said grating lines. 
     
     
       2. A surface wave filter as defined in claim 1, wherein successive grating lines or opposite portions of said lines, at least in one part of the resonator, are disposed at an angle to one another. 
     
     
       3. A surface wave filter as defined in claim 1, wherein at least some of said grating lines are curved. 
     
     
       4. A surface wave filter as defined in claim 1, wherein at least some of said grating lines contain a curved region. 
     
     
       5. A surface wave filter as defined in claim 1, wherein the length of at least some of the grating lines is limited by a curve, preferably an arc of a circle. 
     
     
       6. A surface wave filter as defined in claim 5, wherein said curve comprises an arc of a circle. 
     
     
       7. A surface wave filter, as defined in claim 1, wherein the resonator is coupled to other disturbance locations and a region having a different wave impedance from the resonator and the disturbance location region is disposed between the resonator and the disturbance locations which are to be coupled. 
     
     
       8. A surface wave filter, as defined in claim 1, wherein a matching amplifier is provided at the filter input and/or output and contains at least one transistor, the matching amplifier being disposed in chip form on the substrate. 
     
     
       9. An acoustic surface wave filter comprising a member stimulable to surface oscillation, first means associated with said member for converting electrical energy into mechanical energy, second means associated with said member for converting mechanical energy into electrical energy and a plurality of disturbance locations on a surface of said member in the form of a line grating with spacings between adjacent lines of said grating of varying size in the longitudinal direction of said lines, at least over part of the length of said lines.